Byron Smith re-enters court before the jury made their ruling at the Morrison County Courthouse, Tuesday, April 29, 2014, in Little Falls, Minn. A jury convicted Smith on Tuesday for premeditating the 2012 murders of two teenage cousins who broke into his home.

Atlanta — Two recent cases in Montana and Minnesota where homeowners appeared to set traps before fatally shooting teenage intruders suggest that US society may be drawing some limits on the controversial “stand your ground” defense at the heart of major recent court cases, including the shooting of Trayvon Martin.

A jury convicted Byron Smith of Minnesota on Tuesday for premeditating the 2012 murders of two teenage cousins who broke into his home. And Markus Kaarma of Montana is now facing homicide charges after he allegedly fired a shotgun four times through his garage door on Sunday, when a German exchange student tripped an alarm. The student, a soccer player named Diren Dede, was killed.

The philosophy of self-defense and home defense have deep roots in English common law and more-modern American jurisprudence. In 2005, additional protections for self-defense began to emerge: That year Florida became the first state to expand the castle doctrine – the idea that one’s home is one’s castle – to include public spaces.

In both recent cases, the accused killers invoked self-defense claims, saying they reasonably believed their lives were in danger from intruders. Prosecutors have pressed ahead with the cases – prompting consideration of potential limits to liberalized self-defense laws.

“If somebody breaks into your house in the middle of the night, the presumption is you have the right to assume that they are armed and intend to do you harm,” says criminologist and gun policy expert Edward Leddy, a professor emeritus at St. Leo University in Florida. The question in the Minnesota and Montana cases, he says, is, “How reasonable is that presumption? The problem is there’s no clear-cut answer to that. It depends on the situation and the reasonableness of the person’s fear.”

At least 22 states now have stand your ground laws, according to the National Conference of State Legislatures, but all US states give wide latitude to homeowners who kill intruders, as long as their fears of injury were reasonable. Since the national uproar over the Martin shooting, lawmakers in seven states have attempted unsuccessfully to weaken or even repeal the new breed of self-defense laws.

Studies have failed to determine decisively whether these laws are a reliable check on crime or whether they in fact produce more violence.

Indeed, some ask whether liberalized self-defense laws enable, even encourage, some people to use deadly force.

“The terrible reality is that there’s a certain percentage of the population who do not look at these laws as protection but rather as an opportunity,” says Jonathan Turley, a law professor at George Washington University.

The case in Montana has some similarities to a Louisiana incident in 1992. In that earlier case, a Japanese exchange student, Yoshihiro Hattori, was killed by a scared homeowner in Baton Rouge after he knocked on the door, looking for a Halloween party. However, Louisiana prosecutors declined to file charges.

“The Japanese people were horrified by the fact that this could happen, but they were justifiably more horrified when the man was not charged,” Professor Turley says.

Now, with the death of a German exchange student, a spokeswoman for the German Consulate in San Francisco said, “what happened [was] completely out of proportion to the probable risk.”

But in a potential sign of changing attitudes, prosecutors have decided to go forward with charges in the Montana case. Prosecutors say Mr. Kaarma had told his hairdresser that he was “ready to shoot some [expletive] kid” after getting repeatedly burglarized.

Kaarma, prosecutors say, will have to prove that he could have been killed or seriously hurt by the intruder. “The state doesn’t believe that Kaarma identified Dede as a threat to commit a forcible felony in the garage,” prosecutor Andrew Paul told the Missoulian newspaper in Montana. “He actually sought Dede out by essentially trapping him in the garage.”

Gary Marbut, president of the Montana Shooting Sports Association, who helped draft the Montana self-defense law, defended it this week in the wake of the shooting.

"The justice system is very good at sorting out innocence and guilt – right and wrong and those sorts of things," Mr. Marbut told MTN News, a network of CBS affiliates in Montana. "It needs to be given time to work before determining that the laws are improper or inadequate."

The Minnesota shooting, meanwhile, is similar to a 2007 Texas case in which a man named Joe Horn corralled two burglars outside his home and killed them on the front lawn. Mr. Horn had a clear understanding of changes in the law that protected homeowners, which he discussed with a dispatcher before he went outside and shot the men.

A Texas grand jury refused to bring charges against Horn.

In the Minnesota case, prosecutors told the jury that Mr. Smith moved his truck to make the house look empty. He was watching a surveillance system as he waited in a basement stocked with food, water, and two guns.

In an audio recording he made, Smith can be heard telling the pair whom he shot as they descended stairs into the basement: “You’re dead” and to the other, “You’re dying.”

“To lie in wait for somebody goes against all the principles that castle doctrine is supposed to fulfill, the first one being that we don’t want to encourage people to kill each other,” says Mary Anne Franks, a law professor at the University of Miami. Such laws have “created ambiguity and pushed people in the direction of, ‘Let’s err on the side of lethality.’ ”

Stand your ground laws entered the national discussion with the 2012 killing of Trayvon. Last summer, a Florida jury acquitted George Zimmerman for the murder of Trayvon, even after evidence showed that Mr. Zimmerman stalked the innocent, unarmed teenager before killing him when the two got in a fight.

Other recent cases have also made headlines. Earlier this year, a Jacksonville, Fla., jury found Michael Dunn guilty of attempted murder after he fired into a fleeing SUV, but deadlocked on the charge of murdering a teenager, Jordan Davis, who was killed in the barrage. After arguing with the teenagers over loud music, Mr. Dunn testified he saw a gun and fired in self-defense. Police never found a gun.

A retrial for the murder charge has been indefinitely delayed.

In another case with similarities to the Montana one, a Michigan man, Theodore Wafer, is accused of fatally shooting an unarmed 19-year-old woman, Renisha McBride, late last year after she knocked on his door in the middle of the night. Mr. Wafer, who is claiming he shot in self-defense, is set to go on trial in July for second-degree murder charges.